Modern Distributed Filesystems For Linux: An Introduction - page 3

What Are Distributed Filesystems?

August 7, 2002

By
Bill von Hagen

Using a distributed filesystem introduces new commands and new
concerns for system administrators, but also simplifies many standard
administrative tasks. Distributed computing environments typically
enable users to log in on any workstation within an administrative
domain. This requires that the login, or authentication, mechanism,
also be network-aware. In distributed filesystem environments,
password and group files located on individual machines must be
secondary to networked authentication mechanisms. A network-aware
authentication mechanism, such as Kerberos or NIS, provides users the
flexibiltiy to use any workstation, while standard machine-specific
authentication mechanisms must still exist so that administartors can
log in on individual machines to repair them or perform administrative
tasks.

Storing shared data on centralized file servers rather than on
individual desktop systems simplifies administrative tasks such as
backing up and restoring files and directories. It also centralizes
standard storage administration tasks such as monitoring filesystem
use, and introduces new possibilities for storage management, such as
load balancing. Distributed filesystems such as OpenAFS and
Coda provide built-in logical volume management systems that enable
administrators to move heavily-used volumes to more powerful or
lightly-used machines. If the distributed filesystem supports
replication, copies of heavily-used volumes can be distributed across
multiple fileservers for use by different clients. This can reduce
network use and lighten the load on specific servers. By using logical
volumes rather than disk-specific physical volumes, distributed
filesystems can also make it easy to add storage to your computing
environment while your systems are running, without requiring
downtime.

Using a distributed filesystem also makes it easier to share access to
software, though you have to make sure that your software licenses
enable you to install software into a distributed filesystem. Like the
print servers that were part of the original motivation for
client/server computing, distributed filesystems also simplify sharing
access to specialized hardware by connecting to the system that hosts
the hardware over the network and still being able to see all your
files and data.

Using a centralized distributed filesystem can provide significant
cost and performance benefits for client systems. Distributed
filesystems substantially reduce hardware costs by minimizing the type
and amount of storage that is required on any desktop or
laptop workstation. Using a distributed filesystem as the repository
for user data usually means faster client restart times because much
of the data is no longer stored locally and therefore does not have to
be checked for filesystem consistency after restarting a client. The
combination of a distributed filesystem using a journaling filesystem
for all or most of the filesystems local to client systems can provide
additional improvements in system restart times.